Help: Saving email docs on itouch WITHOUT redownload

Hi everyone,
I know how to get files onto my itouch and view them, but i recently realized when i am offline for a bit then go back online, i have to redownload most of any documents i downloaded for viewing.

Does anyone know how to "store" these files on the itouch so that I can view them without having to be online and download the files each time? (I'm out here in China where the wifi isn't too accessible nor very quick).